Modern fuel injection systems have been used for supplying fuel to gasoline internal combustion engines for automobiles because their ability to precisely meter fuel flow and accurately control the mixture of fuel and air delivered to an engine typically dramatically improves engine performance while reducing engine exhaust gas emissions. In operation, an electric fuel pump transfers gasoline under high pressure directly from a remote gas tank, along a fuel line, and to a fuel rail connected to individual fuel injectors of the fuel injection system. During operation, excess fuel not used by the injectors during periods of low engine demand is returned to the gas tank, while fuel that has vaporized is mixed with air entering the engine or stored in an activated-charcoal canister.
Unfortunately, unused fuel returned to the gas tank can vaporize or become aerated and/or foamy which can lean out the air-fuel mixture delivered to the engine by the fuel pump. Since two cycle engines depend upon a constant predictable stream of fuel mixed with oil to maintain engine temperature, a lean operating condition can cause the engine to stall or, even worse, overheat.
Another problem common to marine engine applications is providing a supply of liquid fuel from the remote fuel tank to the engine. Conventional marine fuel handling systems typically use a paper element water filter in the fuel line between the tank and engine to prevent water in the fuel from entering the engine during operation. As this filter becomes saturated with water it can restrict fuel flow to the engine causing it to run poorly on a lean air-fuel mixture, possibly overheating the engine, or completely block flow causing the engine to stall, possibly stranding a boater far from shore. This type of filter can also collapse or become porous allowing water to pass directly through the filter and into the engine which can damage it.
As a result of more stringent emissions regulations and customer demand for better performance, fuel injection systems for use with marine internal combustion engines are under development. However, because the marine environment differs considerably from vehicle operating environments, considerable challenges are being faced by designers. For example, in applications where it is desired to mate fuel injection to outboard motors, Coast Guard regulations do not allow the use of a pressurized fuel line from the remote gas tank to the engine to prevent fuel from leaking, igniting, and possibly causing injury. Coast Guard regulations also prohibit returning excess fuel not used by the fuel injectors to the gas tank, as is typically done in automotive fuel injection systems.